The present invention relates to the field of optical waveguides and phase modulators for modulating light traveling through the waveguides.
Recently, considerable interest has been shown in the transmission of large amounts of information from many sources to many destinations by means of tiny beams of light transmitted through optical waveguides. Information is modulated upon the tiny beams of light and the beams are thereafter switched appropriately through a network of light guides or fiber optic elements to be routed to desired destinations. Devices for switching the tiny light beams by electronic control involve waveguides surrounded by material of lower refractive index to confine the light. 2.times.2 "X" waveguide switches of the two-mode interference type have a waveguide in the mid-region of the switch whose dimensions are large enough to propagate the two lowest-order modes. The waveguide formed at the intersection of the monomode legs of the "X" type switch utilizes means for controlling the electric field (or free-carrier density) within the guide to in turn cause changes in the index of refraction of various cross-sectional portions of the switch intersection, and as a result, the velocity of propagation of the even mode relative to the odd mode is differentially affected to switch the direction of the output light beam. Our U.S. Pat. No. 4,693,547 teaches utilizing an LED for switching control and our U.S. Pat. Nos. 4,746,183, 4,787,691, and 4,728,167, incorporated by reference herein, teach utilizing pn junctions to inject free carriers into the waveguide at the X-switch intersection. However, the generation of heat due to the high resulting I.sup.2 R losses and the dissipation of electrical power is undesirable.